oracle decode usage is "DECODE(expression, condition 1, result 1, condition 2, result 2, ..., default result)", the expression is the field or expression to be compared, which can be A value of any data type that is compared with a condition in turn. The condition can be a field or a constant, and the result can be a field, a constant, or an expression. When an expression is equal to a condition, the DECODE function returns the result corresponding to the condition.
#The operating environment of this article: Windows 10 system, Oracle version 19c, dell g3 computer.
The DECODE function in Oracle is a conditional expression function, its main function is to return the corresponding result according to the given conditions. It is similar to switch statement or if-else statement in other programming languages. The DECODE function accepts multiple parameters, performs calculations according to specific rules, and returns a result. The usage of the DECODE function will be introduced in detail below.
The basic usage of the DECODE function is as follows:
DECODE(expression, condition 1, result 1, condition 2, result 2, ..., default result)
Expression The formula is the field or expression to be compared, which can be a value of any data type. It is compared with the condition in turn. The condition can be a field or a constant, and the result can be a field, a constant, or an expression. When an expression is equal to a condition, the DECODE function returns the result corresponding to the condition. If the expression is not equal to all conditions, the DECODE function returns a default result. It should be noted that the DECODE function can only be used for equality comparison and cannot perform other comparison operations (such as greater than, less than, etc.).
The following is an example of a DECODE function:
SELECT last_name, salary, DECODE(job_id, 'IT_PROG', salary * 1.1, 'SA_REP', salary * 1.2, salary) AS new_salary FROM employees;
The above query will return the employee's last name, salary and calculate new wages based on different jobs. If the employee's job position is 'IT_PROG', the new salary is 1.1 times the original salary; if it is 'SA_REP', the new salary is 1.2 times the original salary; for employees in other jobs, the new salary is equal to the original salary.
The DECODE function can also perform comparisons based on multiple conditions. In this case, multiple condition and result pairs can be used, and the order of comparison is performed in the order of parameters. For example:
SELECT last_name, job_id, DECODE(job_id, 'IT_PROG', 'IT', 'SA_REP', 'Sales', 'HR_REP', 'HR', 'OTHER') AS department FROM employees;
The above query will return the employee's last name, job position, and the corresponding department name according to different job positions. At this time, if the employee's job position is 'IT_PROG', then 'IT' is returned; if it is 'SA_REP', then 'Sales' is returned; if it is 'HR_REP', then 'HR' is returned; for other jobs, 'OTHER' is returned .
Summary
DECODE function is a very commonly used conditional expression function in Oracle, which can return different results according to different conditions. It is flexible and concise, and can handle various conditional judgments and return correct results. In actual queries, the DECODE function is often used for field value conversion, data cleaning, condition judgment, etc., which greatly facilitates data processing and analysis
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